Method of producing gas for the carburization of steel



Aug. -1o, 1937. J. A. Dow 2,089,545

METHOD OF PRODUCING GAS FOR THE CARBURIZATION OF STEEL Filed July 12, 1955 INVENToR. l J6??? f2' Ud/V.

W Z/Z.

ATTORNEY.

Patented Aug. l0, 1937 UNITED STATES PATENT OFFICE METHOD OF PRODUCING GAS FOR THE CARBURIZATION F STEEL This invention relates to method of making gaseous mixture for carburizing steel parts.

The object of the invention is to provide a diluent gas with which a hydrocarbon gas such as propane may be mixedthe mixture to be capable of carburizing steel parts and without depositing or forming an appreciable amount of soot or -carbon on the steel surfaces at the same time.

'Ihe diluent gas is free of decarburizlng effect on medium and high carbon steels and is found useful as a protective medium when annealing and hardening parts of these steels.

It is therefore an object of this invention to provide a commercially inexpensive diluent gas which will have neither a carburizing nor decarburizing effect on high carbon steel but consists principally of gases neutral to such steelviz., nitrogen, carbon monoxide, hydrogen-and to which a low quantity of a hydrocarbon gase. g., ethane, propane, butane, various unsaturated hydrocarbons pure or in mixtures-is added to secure the carburizing effect as is hereinafter described.

It is also an object of the invention to so regulate the dilution of the heavy hydrocarbons and the rate of ow of the mixture that the rate of chemical breakdown liberating carbon may be so retarded as to distribute the resultant carburizing action substantially uniformly throughout the carburizing chamber or zone of a furnace and without formation of an appreciable or objectionable amount of soot on the steels being carburized-all of which is hereinafter more fully described and claimed.

The commercially available gases for carburizing contain one or more of the gases in each of the three following classes:

(l) Heavy hydro-carbons-ethane, propane, 4U butane and like unsaturated hydro-carbons which all undoubtedly tend to break down under heat and give up carbon at a faster rate than it can be absorbed by the steel in the carburlzing chamber. These gases cannot be successfully used undiluted since at the rate of flow normally required in the carburizing chamber, the parts being carburized become heavily coated with soot or coke.

(2) Neutral gases such as nitrogen, carbon monoxide, hydrogen, methane, etc. These gases are all alike in that, under the rates of ow commercially practicable, these gases have little or no carburizing effect, do not deposit soot and do not have any appreciable d ecarburizing effect.

(3) Decarburizing agents such as carbon d ioxide, water vapor, oxygen. These gases are all alike in that small percentages in a gaseous mixture have a pronounced decarburizing tendency heretofore commonly overcome by addition of certain percentages of the heavy hydro-carbons of class l.

It is now the commercial practice to feed a gas containing one or more of the gases of each of the three groups as a mixture into a furnace retort, the percentage of the class 1 gases being suicient to counteract the class 3 gases present and in addition to supply the necessary carbon for carburization of steel.

However, in such previous commercial practice, it has been found that a soot deposit will occur on the furnace walls and the steel under treatment, due undoubtedly to the interaction of the class l and class 3 gases even though the percentage of class 1 gases present is insuiilcient to produce the most rapid carburization and the desired carbon content of the case on the parts under treatment.

This invention therefore seeks to avoid the soot deposit, to secure an inexpensive diluent gas free from decarburizing agents and consisting of a neutral gas in major proportions and a small quantity of heavy hydro-carbon gas sufficient to accomplish the carburizin'g in the following percentages:

High Low range range Neutral gasu 99.5% Hydrocarbon gas 15% .5%

These percentages of the neutral and hydrocarbon gases will vary somewhat depending upon the specific hydro-carbon gas utilized but the percentage in any case will usually be between the above stated high and low range. Such a gas may be obtained in a number of ways but the gas hereinafter described has not within my knowledge been produced and utilized as a carburizing agent for the treatment of steels to provide a case-hardened steel Without deposition of soot in objectionable quantity.

The preferred method of obtaining the gas is through utilization of the following elements shown in the accompanying drawing:

A blower is provided at I taking air and gas from the intake pipe 2 and .discharging through the pipe 3 into the heated retort 4. In this retort is a series of small particles 5 such as pieces of brick or the like and of such size as to prodeposited. The gas that is drawn into the intake may be of any of the commercial fuel gases such as a manufactured city gas, propane, natural gas etc. This gas should be so regulated that the products of partial combustion contain not more than 3 per cent hydro-carbons or more than 5 per cent carbon dioxide. Into the gas ow, air is drawn through the valved inlet 6, the gas and airbeing in the approximate proportions of two parts of gas tothree parts of air in the case of manufactured city gas. The `air should be generally in the proportion of from one-fourth to one-half the air required for complete combustion. 'I'hese gases in mixture pass through the retort I to a condenser "I, which may be any approved form of air, water, or refrigerated type ofcondenser.` In the type here shown, cold water is supplied to the interior of the condenser housing and gases pass downwardly through the coil 8 and, due to this chilling of the gases, the water Vapor is condensed and may ilow oif through the drain 9 opening to the conduit exteriorly of the condenser as shown. At I is shown another heated retort which is Within an outer chamber and'to the upper end of which a conduit from the condenser discharges. In this retort is a bed formed of charcoal, coke, graphite, charred bone or the like and preferably, although not necessarily, treated with sodium or barium carbonates or like suitable activating agent. 'I'he term carbonaceous .material as used in the appended claims refers to the above listed character of materials, or material productive of like result. 'Ihis charcoal is supported on a grating II providing a space at the bottom of the retort I0 to whichis connected the outlet conduit I2.

In this retort the carbon dioxide and such Water vapor as may be present in the gas enter- 40 ing the same are removed to such extent that theirremaining percentages when added together do not exceed 1 per cent of the total by volume. In actual practice, when operating at a temperature of about 1750 degrees F., I have been able to remove these gases to such extent 5 ,ingy between 1400'and 1600 degrees Fahrenheit and in this state after passing from the retort I0 may be used for producing a thin case on such low or medium carbon steels at their normalhardening temperature `heretofore usually performed by submitting such steels to molten cyanide. Also, this gas as it comes from the retort I Il may be used as a protective'medium in the hardening of high carbon steels or carburized steel parts and such gas may be manufactured by passing air or steam through the heated charcoal chamber I0. The advantage of the units 4 and 'I is that the amount of carbonaceous material used up in the retort II) in producing 1,000 cubic feet of gas is much reduced.

It is pointed out that the retort I0 is heated by heating the interior of the chamber in any 75 tort Ill is sealed to these combustion gases in.

through a conduit I6 within which there is a` small orice Il and gage I8 arranged to measure the ow of the heavy hydro-carbon gas. This conduit I6 has a valve I9 for controlling the volume of ilow in order that the desired percentage of heavy hydro-carbon gas being utilized is discharged into the carburizing retort I5 in `which the steel parts are positioned for treatment. The percentage of dilution of the hydrocarbon gas by the prepared gas passing throughr the conduit I2 and the rate of ow used depends on the size of the carburizing furnace or retort, its operating temperature and to a lesser extent the character of the parts to be carburized. With this furnace it is possible to sc dilute hydrocarbon gas with the gas passing from the retort I 0 to the conduit I2 that carburizing is accomplished in the carburizing furnace or retort with practically no deposition of soot and wherein it is inmaterial whether the chamber be full of material to be carburized or only partially loaded.

It is pointed out that the carbonaceous material in the retort I 0 is uniformly heated in that portion through which the gases are passed and the gas heated to a temperature above that at which reverse reactions may occur. 'I'he gas is then removed from the heated carbonaceous material through a relatively small outlet pipe and is therefore chilled before any material reverse reactions take place which would again introduce de-carburizing agents.

From the foregoing it'will be evident that the invention involves the diluting of a vhydro-carbon gas of class 1 type with an inexpensive diluent gas substantially free from decarburizing agents of the class 3 typein order to secure a carburiz- `ing gas free of objectionable soot depositing tendency in the carburizing chamber for the exact degree of carburization desired.

In explanation of the use of class l type of gases with a diluent gas vof class 3 heretofore mentioned, it is pointed out that-while hydrogen is a de-carburlzing agent, pure dry hydrogen decarburizes so slowly that it can be neglected in commercial practice, the rate being approximately one thousandth of an inch in twentyfour hours, and also that methane is a carburizing agent but in my experience breaks down under heatA so slowly that in the absence of other hydro-carbons, an inferior low carbon case only can be produced on steel and that, in my experience, a small percentage of ethane or propane is more active than high percentages of methane Any hydro-carbon which in a carburizing gas. breaks down under heat at a rate suiciently rapid to be suitable for carburizing steel is herein termed an active or heavy hydro-carbon and Would be grouped in class 1. It is also known that `carbon monoxide is an active carburizing agent but in its commercial application so little carbon is available per cubic foot of carbon monoxide that impractically large quantities of gas are required for a commercial carburizing furnace. The available carbon per cubic foot is small because as carbon monoxide'gives up its carbon to steel, carbon dioxide is formed and only a small percentage of this gas will counteract the carbon monoxide.

The essence of the process and application thereof is that all active de-carburizing agents low as 1 to 5 percent produces an active carburizing gas, whereas if small percentages of water vapor and carbon dioxide are present and not neutralized, it is necessary to add as high as 20 per cent propane to accomplish the same result. These relative low percentages of active l hydro-carbon gas utilized in my composition do not cause detrimental soot deposit on the steel being treated and yet carburizes actively and at a rapid rate, if the de-carburizing agents are present only in such quantity as to be in practical equilibrium with the carbon monoxide and hydrogen present and carbon at carburizing temperatures. It is further pointed out that the chamber I0 containing carbonaceous material is mounted within the heating chamber, its base being above the base of the chamber and having a grating Il supporting the charcoal above the base of the retort. The gas passing downwardly through the carbonaceous material is under the high heat of the furnace not in contact with a wall thereof or subject to influence of temperature of atmosphere while in the chamber and thus not in position to be cooled. 'I'he flow through the bed is comparatively slow through the hottest part of the carbonaceous chamber retort and then passes through the conduit I2 of comparatively small cross sectional area in which the movement is rapid. Therefore, chilling of the gas is immediate and not slow thus allowing no measurable change in the gas composition in its passage from the hottest p'art of the retort. The effect of frozen equilibrium" is therefore obtained.

Gas produced of thepcomposition described, in which the dilution of the hydro-carbon gas is regulated, makes it possible that the rate of chemical break-down which liberates carbon in the carburizing furnace may be so retarded that the chemical break-down is distributed throughout the full length of the carburizing chamber or zone of the furnace.

It is also evident from the foregoing that the invention is not restricted to the specic apparatus utilized and that various characters of apparatus may be utilized to secure a gas having the carburizing properties herein described without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim:-

1. The method of producing a gas for carburizing low or medium carbon steels consisting in rst exposing a gaseous mixture to reaction with carbonaceous material in a heated chamber until the carbon dioxide and water vapor present or formed are reduced to such proportions as to be in practical chemical equilibrium with the carbon monoxide and hydrogen present and carbon at carburizing temperatures. removing the gases from the carbonaceous material at a temperature above that at which reverse reactions may take place, rapidly chilling the gases to a temperature below that at which reverse reactions may take place, and then adding an active hydro-carbon gas thereto in quantity not to exceed 10 per cent of the total volume of the mixed gases.

2. The method of producing a gas for carburizing low or medium carbon steels consisting in rst exposing a gaseous mixture to reaction with carbonaceous material in a heated chamber until the carbon dioxide and water vapor present or formed are reduced to such proportions as to be in practical chemical equilibrium with the carbon monoxide and hydrogen present and carbon at carburizing temperatures, removing the gases from the carbonaceous -material at a temperature above that at which reverse reactions may take place, rapidly chilling the gases to a temperature below that at which reverse reactions may take place, and then adding thereto active hydro-carbon gas in volume productive of the case characteristics desired on the steel being carburized.

3. The method of producing a gas for carburizing low or medium carbon steels consisting in iirst exposing a gaseous mixture containing carbon dioxide, carbon monoxide. water vapor and hydrogen to contact with carbonaceous material in a heated chamber until the carbon dioxide and water vapor content are reduced to such proportion as to be in practical chemical equilibrium with the carbon monoxide and hydrogen present and carbon at carburizing temperatures, removing the gases from the carbonaceous material at a temperature above that at which reverse reactions may take place, rapidly chilling the gases to a temperature below that at which reverse reactions may take place, and then adding thereto an active hydro-carbon gas in volume less than is productive of detrimental soot deposit on the steel by carburizing.

JOHN A. DOW. 

